Two sided runway marker

ABSTRACT

A runway marker has a pair of upwardly converging reflectant planar panels facing approximately in opposite directions. In its correct attitude on a support surface the panels slope at 2 DEG -6 DEG  to the vertical if the marker is intended for assisting the landing of fixed wing aircraft and at 8 DEG -10 DEG  to the vertical if the marker is intended for assisting the landing of helicopters. The reflectant panels are preferably retroreflectant.

This application is a continuation-in-part of application Ser. No.07/775,751 filed on Oct. 15, 1991 now U.S. Pat. No. 5,223,977, which inturn, is a continuation-in-part of application Ser. No. 07/617,766 filedon Nov. 26, 1990, now U.S. Pat. No. 5,115,343.

This invention relates to a marker for use in marking unlighted runwaysor helicopter landing pads in remote areas.

There is a considerable need for a cheap and efficient reflector markerfor remote runways which may be located in areas without a practicallyavailable source of power. Such a cheap and efficient reflector markermay also be required as back up, for use on a normally lighted runway,in case of power failure. There is an analogous need for helicopter padmarkers.

The invention provides an economical and efficient runway marker forfixed wing aircraft and helicopters, having means for mounting themarker on a support surface adjacent a runway in a predeterminedattitude. The marker has a pair of substantially planar panels joined toface in approximately opposite directions. Each panel extends upwardlyand slopes toward the other and slopes at an angle of about 4°-12° tothe other panel, for fixed wing aircraft, whereby the reflector may bemounted in said attitude with the panels each sloping at 2°-6° to thevertical, a substantial part of each of said surfaces beingretroreflectant. (For helicopters the panels will converge at 16° -20°and slope at 8°-10° to the vertical when in the desired attitude).

By retroreflection herein is meant reflection back toward the source ofthe incident ray.

There is thus provided a convenient runway marker which may be mountedon the support surface to be at 2°-6° to the horizontal to correspond tothe preferred 3° descent angle for fixed wing aircraft, and with thenormals to the planar surfaces directed in a vertical plane parallel tothe runway, so that a plane on a landing approach with its landinglights or a spotlight on, will receive the brightest retroreflectionwhen descending in line with the runway and at a 2°-6° descendingapproach path. Since reflectant surfaces of specific qualities arediscussed hereafter, it is noted that an ordinary retroreflectantsurface will give (to the pilot) a higher retroreflection when the beamis incident normal to the reflecting surface, than when the beam'sdirection of incidence is non-normal. The support surface for the markermay be a specifically provided base, or a base provided for otherpurposes. Or ground levelling means may be provided to achieve thedesired orientation for the retroreflecting surface.

The invention is described mainly with reference to the marker for fixedwing aircraft and their landing strips, where the retroreflecting panelsslope at angles of between and 2°6° to the vertical. However, it shouldbe realized that the invention as disclosed throughout applies where thepanels slope at between 8°-10° to the vertical for use with helicoptersand in combination with helicopter landing pads.

In a preferred aspect of the invention, the reflectant area is coveredwith retroreflecting material which gives a brighter retroreflection forincident light normal to the plane of the reflector than itsretroreflection for light incident at another angle. Thusretroreflecting material and normally reflecting material will give ahigher degree of retroreflectivity to normally incident light but therelative drop in retroreflectivity, for non-normal angles of incidentlight, will be greater than with ordinary retroreflective material. Thusfor aircraft approaching the marker from directions other than normal toa reflectant area, the marker with retroreflectant material is easierfor the pilot to detect.

With retroreflectant material, the pilot of an approaching aircraftreceives, whatever his approach angle, a brighter reflection of hislanding lights than with an ordinary reflector, and, because of aquality of the preferred retroreflector, receives the brightestreflection when he is on the correct approach path. Thus the pilot mayuse the reflection intensity as his guide toward finding and followingthe correct path.

By the term `aluminum` herein, including in the claims, I mean toinclude alloys of aluminum.

In a preferred aspect of the invention the panels carrying theretroreflectant material, (and preferably the whole marker (other thanthe retroreflectant layers)) are made of aluminum. A particularadvantage of aluminum in this invention is that aluminum has nearly thesame coefficient of thermal expansion as the preferred retroreflectantmaterial (polycarbonate with aluminized coating) which is preferablyapplied as a layer to the panel. The preferred retroreflectant materialis an aluminized polycarbonate tape sold under the trademark Reflexire.Considering the, fact that the reflector in accord with the inventionshould be designed to withstand a temperature range of -40° C. to +50°C., the effects of differential thermal expansion between the body ofthe reflector and the reflectant surface are material and in manysituations, the use of aluminum or aluminum alloys is found the best wayto avoid buckling or tearing of the retroreflectant material, since thethermal expansion coefficient of aluminum or aluminum alloys is close tothat of the preferred retroreflectant material.

By `aluminum` hereafter, Including the claims, I mean to includealuminum alloys.

In a preferred aspect of the invention there is, on each panel, inaddition to the retroreflectant area, at least one stripe (andpreferably two) of fluorescent material. The fluorescent stripe orstripes is designed to give a significant daytime indication to thepilot of the presence and (considering a number of markers collectively)of the direction of the runway. The retroreflectant material tends togive a flat impression, not easily noticeable by the pilot whenilluminated by sunlight (except when the pilot is aligned with the sunand the material) or daylight.

In a preferred embodiment of the invention each of the planar panels isformed of a sheet of material, preferably aluminum, where the panelIntegrally extends into side walls generally perpendicular to saidpanels, and means are provided for Joining each side wall of a panel tothe adjacent side wall of the opposite panel. Preferably each panel sidewall will be provided with a inwardly directed flange at its inner endgenerally perpendicular to the side wall and (at the desired relativeangles o the panels) parallel to the flange on the side wall to which Itis to be Joined. Thus each flange of one side wall of one panel maysimply bolted or otherwise attached to the flange of the appropriateside wall of the other panel, to produce the body of the reflector.

In a preferred form of the invention the planar panels, in addition toconverging upwardly toward each other also converge in plan from one endtoward the other to provide a toed-in effect. Thus with the devicemounted on the support surface in its desired attitude, horizontalplanes intersect the respective panels, on lines which converge relativeto each other at small angles, and preferably at less than 6%. Theresult is that the toed-in markers may be arranged on each side of therunway and will give a brighter retroreflection to a pilot when he isdescending along a line centered over the runway than when he is on oneside or the other of such centered line. A pilot approaching the runway,on a correct line will receive a brighter reflection at points neartouch down, with the toed-in markers than with inventive markers whichare not `toed-in`.

The body of the marker, thus produced, may be provided with anchoringmeans, and, if desired, a top member. The anchoring means may be of anydesign, adapted to establish attachment to the support surface andprovide the correct azimuthal orientation of the marker and to providethe correct attitude, implying correct slope of the panel sides relativeto the vertical. Preferably I provide a base plate with side flangeswhich attach to lower portions of the side walls of the joined body. Thebase plate may then be mounted on the support (in this case, the ground)surface beside the runway or on the runway by such means as spikesinserted into the surface or by bolting to a pre-installed base. Shimsmay be used with the spikes or bolts to achieve the correct attitudeand, in addition, the marker must be installed in the correct azimuthalorientation.

In drawings which illustrate a preferred embodiment of the invention:

FIG. 1 shows inventive markers marking a runway,

FIG. 2 shows an assembled marker,

FIG. 3 shows the marker of FIG. 2 in exploded view,

FIG. 4 shows a broken-away view of an assembled marker,

FIG. 5 shows an alternative construction for the marker base.

FIG. 6-8 show preferred retroreflectant material

FIG. 9 shows a modified from of the inventive marker

FIG. 10 shows a runway marked with the marker of FIG. 9; and

FIG. 11 shows a frangible mount for the marker.

In the preferred embodiment of the invention:

FIG. 1 shows a runway for fixed wing aircraft marked with 6 markers 10in accord with the invention, arranged three on each side of the runwayin respectively spaced locations. The markers are mounted on a supportsurface which may be the ground itself or a specifically constructedbase in its predetermined attitude both relative to the vertical and toazimuthal directions. Each marker has a pair of outwardly facingreflecting panels 12 each converging upwardly with (in correct attitude)a slope to the vertical of 2°-6° and, in azimuth, oriented so that avertical plane parallel to the latitudinal direction of the runway isperpendicular to the planes of the reflecting surfaces of the panels.

Each marker has two planar panels 12. In the preferred construction eachpanel extends integrally on each side into side walls 14 preferablygenerally perpendicular to the panels and extending along their height.The side walls are each provided with inwardly turned flanges 16perpendicular to the side walls and arranged so that the flange 16 ofthe side wall of one panel may be parallel to and Juxtaposed to theflange 16 of the appropriate side wall of the other panel. Registeringbolt holes 18 are provided in the flanges so that each abutting pair offlanges may be bolted together to form the completed marker body. Thepanels 10 and side walls 14 are made of aluminum thick enough to be selfsustaining.

The body as shown is preferably provided with a base plate 18', formounting the pane can support surface. The base plate 18' is preferablymade of aluminum thick enough to be self sustaining and dimensioned toconform to the area defined by the opposed lower edges of the panels andthe opposed lower edges of respective pairs of joined side walls. Thebase is provided with upstanding flanges 20 at opposed edges selected tooverlie the outer surfaces of the side walls for attachment thereto,preferably, where aluminum is used, by self tapping screws 22. The baseplate is preferably provided with apertures 24 for anchoring means. InFIG. 3 the mode of attachment for anchoring is by spikes 26 and thesupport surface is the ground beside the runway. The azimuthalorientation of the marker must be selected so that vertical planesthrough the planar panels are aligned with the runway. The attitude ofthe marker to ensure the correct angle or the panels to the vertical isthen adjusted by the use or appropriately selected shims 28 in the formof washers about selected spikes. In FIG. 5 the base plate is providedwith a bolt hole 24B and an arcuate slot 24A about the bolt hole orreceiving bolts 30 poured concrete base which then forms the supportsurface. The arcuate slot allows orientation of the marker to achievethe desired azimuthal orientation and shims 28A may be used about ode orthe bolts to achieve the desired attitude. The levelling of a marker inits correct attitude may however be performed by other to moresophisticated methods than those shown.

The marker may be provided with a top plate 34 having four side flanges36 adapted to overlie the top edges of the panels 10 and side walls 14.The top plate may be attached by self tapping screws 40 throughregistering apertures 38 and 42.

Top plate 34 and base 18' may also be made of thick enough to sustainits shape. Top plate 34 and base 18' may each be provided with anaperture 44 (the apertures are vertically aligned) to receive thestandard of a marker flag.

The panels 10 will, over most of their area, be covered withretroreflecting material 46. I prefer to use a plastic provided with analuminized coating defining an array of recessed cube corners. Such aretroreflecting material will, from relatively wide angles to thenormal, retroreflect light from the landing lights (or searchlight) of adescending aircraft. However such retroreflector has a further qualityof importance in the preferred form of the invention. Theretroreflection at large angles to the normal, of the preferred recessedcube corner reflector, is relatively good but retroreflection isstrongest when the incident (and hence the reflected) beam are normal tothe surface. Thus the pilot, of a descending aircraft may tell when heis on the correct descent path by the fact that the retroreflection froma panel becomes brighter or less bright as he approaches or departs fromthe descent angle normal to the panel.

I prefer to use a cube corner recessed retroreflector formed of plasticwith the cube corner recesses molded in a selectively colored aluminizedreflector coating on the outer cube surface. In the preferred form ofsuch material the recessed cube surfaces are covered with a protectivetransparent smooth layer (not shown) also of plastic to protect and keepclean the recessed cube.

As the retroreflectant material, I prefer to use surfaces made up of thecube reflectors as described in the following U.S. Patents:

    ______________________________________                                               2,380,447    Jungerson                                                        3,712,706    Stamm                                                            3,684,348    Rowland                                                          3,810,804    Rowland                                                          4,025,159    McGrath                                                          4,202,600    Burke                                                     ______________________________________                                    

The teachings of the above patents are incorporated herein by reference.

In particular the invention preferably makes use of cube cornerreflective sheeting as described in the Burke U.S. Pat. No. 4,202,600where regular arrays of cube corner reflectors in sheets are arranged inzones (indistinguishable to the user) oriented relative to adjacentzones in such a way that retroreflective intensity variation withazimuthal angle (measured in the plane of the sheet), is reduced at highangles of incidence to the normal to the sheet.

By an array is meant an ordered group of cube corner triads. A `zone` isthe area occupied by such an array.

The invention takes advantage of the fact that retroreflectant materialcomposed of arrays of cube corner reflectors (which are not individuallydistinguishable at minimum expected viewing distances) customarilyretroreflect incident light more strongly at a normal angle of incidencethan at any other angle of incidence.

It is noted that with all cube corner reflector arrays there is somedirectivity in the strength of the secondary reflection. That is for agiven array zone the secondary reflection will be stronger in someazimuthal directions relative to the normal than others. This is ofcourse more noticeable with a single array where all triads have anordered orientation relative to each other. It will also be noted thatthe cube corner reflector array zones which are taught by U.S. Pat. No.4, 202,600 and preferred for use with the invention, are too small forresolution by the viewer so that the actual orientation of individualzones of the reflecting surface is not known when a sheet bearing thereflectant coating is applied. Thus it is preferable if the cube cornerreflector sheet is divided into zones (indistinguishable at usualviewing distances) which are differently oriented relative to each othertending to give a more uniform reflection at large angles to the normaland at varying azimuthal angles about the normal.

Preferably the cube corner cavity material is that sold under the trademark REFLEXITE, a product of the Reflexire Corporation of New Britain,Conn. Such material is a polycarbonate with an aluminized coating. Insuch product the cube corner cavities are arranged in windows formed bytriads of mutually perpendicular cube faces in an ordered array with apredetermined orientation. Such ordered arrays are in zones small enoughto be indistinguishable to the viewer at minimum normal viewingdistances. The zones are preferably arranged to have two orientations at90° to each other arranged in a checkerboard or other pattern. TheREFLEXITE material customarily is supplied in rolls with a self adherentbacking.

FIGS. 6-8 are taken from U.S. Pat. No. 2,202,600 previously referred to.In FIG. 6 the preferred retroreflective sheeting is schematicallyillustrated from the non-retroreflecting side. The array as oriented inFIG. 6 may be thought of as having an orientation corresponding to ahorizontal directional arrow. As stated in U.S. Pat. No. 4,202,600 theorientation of an array with an orientation as shown in FIG. 6 can bevaried in a regularly alternating pattern, such as a checkerboardpattern, in a random pattern or in any other pattern that providessufficient mixing of different orientations to give the sheet anappearance of uniform brightness when viewed at a high angle ofincidence from the minimum.

FIGS. 7 and 8 show two preferred methods of combining arrays in zoneswith orientations at 90° to each other. Since the arrays have 60°symmetry (90°-60°=30°) each zone has its cube corner reflectors orientedat 30° to adjacent zones. The result is reflective sheeting which forretroreflected rays at 60° to the normal, has relatively evenreflectivity at different azimuthal angles about the normal.

As previously stated the preferred sheeting of the Reflexite Corporationof New Britain, Conn. The zones are indistinguishable at normal minimumviewing distance.

It is noted that the two qualities of the preferred material which areof principal value with this invention, are that the nightretroreflection at relatively wide angles to the normal to the planeallows the pilot, at night, to find the general location of the runwayand its markers, while the stronger retroreflection when the pilot is onhis correct descent path acts as an indicator to help him to reach andmaintain the correct descent path.

The preferred retroreflecting material is customarily supplied in rolls,from which the may be cut for adhesive application to panels 10 to form,as shaped by the planar panels, a substantial planar retroreflectingarea 46. Such area will be principally used at night and I prefer to useretroreflecting material of silver color.

Since the marker should be designed to operate over a temperature rangeof -50° to 40° C., it is of some importance that the thermal expansioncoefficient of the retroreflectant layer be close to that of the panels10. With the preferred retroreflecting material as described above theplanar panel is preferably made of aluminum since its coefficient ofthermal expansion is sufficiently close to that of the preferred"Reflexire" as to prevent, in most circumstances, the buckling ortearing of the `Reflexire` over the above temperature range.

In this embodiment it is preferred to make the marker other than thereflecting layer or layers of a single piece of aluminum sheet, ofsufficient thickness to sustain its shape and bent to form the panels10, side walls 14 and flanges 16 as described.

Although the retroreflectant material works excellently at night whenilluminated by the searchlight or landing light of an aircraft, suchmaterial is difficult to distinguish in sunlight or ambient daylightwhich, of course, is not normally retroreflected to the pilot.Accordingly, it is preferred to provide at least one and preferablyupper and lower stripes 48 of fluorescent material, above and below eacharea 10 and oriented to be horizontal in the preferred attitude of themarker. Such bars are preferably formed of self-adhesive fluorescenttape of color contrasting with that of area 46 (fluorescent orange ispreferred for stripes 48) and overlying each panel 10 above and beloweach area 46 (as shown) and alternatively the material forming area 46may be cut to cover the whole area of panel 10, and the upper and lowerfluorescent stripes 48 placed thereover.

There is thus provided, for daytime use, the marker with two horizontalstripes 48 which assist the pilot in locating the runway, and itsazimuthal orientation, and to indicate horizontal indications indirections transverse to the runway. The bars 48 of course do notstrongly retroreflect nor do they give the pilot an indication ofwhether he is descending at the correct angle. They are however usefulin the daytime when the retroreflectant material looks dull under solaror ambient light illumination.

The embodiment of FIG. 5 shows a poured concrete base 50 which would belocated beside the runway and which has a pair of upstanding bolts 30.The base 18A is rotated about the bolt through hole 24B until thecorrect azimuthal orientation is obtained, and then the nuts 52 aretightened to fix the tray firmly in place. The marker is then installedon the tray as described in connection with FIG. 3 and 4.

It should be said that any method of anchoring to a support surface andlevelling the marker thereon is within the scope of the invention.

The preferred embodiment has been described with angular slope of thepanels 10 suitable for fixed wing aircraft. This is believed to be theprincipal use of the invention.

However the invention may also be used to mark helicopter pads andlaunching areas. For use with helicopters, the panels 10 and theirretroreflective material should converge at 16°-20° and, in the correctmarker attitude slope at 8°-10° to the vertical, corresponding to thedesired helicopter descent angle. The panels will, in use, be orientedto be perpendicular to a vertical plane extending in the desiredazimuthal approach direction.

FIG. 9 shows a form 11 of the marker which is a modified alternative tothat shown in FIG. 2. FIG. 9 shows that the members 10A, 14A, 34A(corresponding in function to members 10, 14 and 34 are so proportionedthat opposite faces of the planar panel slope toward each other at anangle A to the vertical as with the panel of FIG. 2. This for FIG. 9 (orFIG. 2) the angle A is 2°-6° for aircraft and 8°-10° for helicopters.FIG. 9 further shows that it is preferred to have the planar panels`toed-in` toward each other by the angle B (making the angle ofconvergence 2B). For most applications B will equal about 1°. Althoughsuch covergence is best shown only at the top of the marker, the planarpanels are arranged so that they converge at substantially the sameangle in any horizontal section through the marker. FIG. 10 shows, inplan, a plurality of the markers of FIG. 9. The advantage of the toed-inarrangement will be obvious from FIG. 10. Thus, as shown, the toe-in isachieved by orienting the planar panels so that vertical planesperpendicular to the panels intersect at an angle of greater than 0° andless than 6° that is between 0° and 60°). Thus, as shown, the toed-inmarkers will tend to self retro-reflect from each side of the runwaytoward an aircraft approaching along the center of the runway axis, andclose to `touch down` more clearly than would markers as in FIG. 2 wherethe vertical planes, normal to the planar panels are parallel to eachother.

Thus in the alternative of FIGS. 9 and 10 the toed-in planar panels 10Amay be provided with central retroreflecting layers 46 bordered by upperand lower fluorescent stripes 48 as in the embodiment of FIGS. 2 and 3.

FIG. 9 also illustrates the provision of a marker pennant 66 on astandard 68 which passes through upper aperture 44 to seat on a spring70 which rests in lower aperture 44.

FIG. 11 demonstrates that the reflecting marker constructed as describedin relation to either FIG. 2 or FIG. 9 may be mounted on a frangiblestandard 60 of plastic which is molded to provide an easily frangiblenarrowing 62. The Frangible standard is mounted in a base 64 in anyconventional manner while the base may be embedded in the ground besidea runway or may be free standing. The provision of the frangible mountmeans that, if a marker is struck by an errant aircraft, it may breakoff with less damage to the aircraft than would a fixed marker.

The various embodiments show retroreflecting material 46 on the twosloping sides 10 bordered by upper and lower fluorescent strips 48. Itis understood that, if desired, end walls 14 or 14A may be provided witha similar arrangement having a central area of retroreflectant materialsimilar to material 46 bordered by upper and lower stripes offluorescent material similar to strips 48.

FIG. 10 indicates, in dotted form, that markers 11 may be arrayed acrosseach end of the runway, to indicate the runway limits.

I claim:
 1. In combination, an aircraft runway, marker therefor, and asupport surface for said marker, comprising:means for mounting saidmarker on said support surface in a predetermined attitude, said marker,when so mounted, comprising a pair of panels facing approximately awayfrom each other in azimuthal directions, said panels sloping upwardlytoward each other at an angle of between 2° and 6° to the vertical, andhaving retroreflectant material covering a substantial area of saidpanels, wherein said marker is shaped so that, when mounted in saidattitude vertical planes through said panels, and perpendicular thereto,intersect at more than 0° and less than 6° to each other.
 2. Thecombination as claimed in claim 1 wherein said panels are formed ofaluminum thick enough to be self sustaining and said retroreflectantmaterial is a layer attached to the outwardly facing surfaces of saidpanels.
 3. The combination as claimed in claim 1 wherein said materialis formed by cube corner cavities and has a higher retroreflectivity forlight incident normal to the plane of the panel and a substantial butlower retroreflectivity for light incident at angles other than normalto said panels.